My impression from the way Sir Walter talks of Admiral Baldwin is its' an indication of his aloof snobbery.
He objects to the navy on two counts; it allows men of lowly birth to achieve eminence 'I was to give place to Lord St. Ives and a certain Admiral Baldwin...' (ch.3)
Sir Walter resents the navy as he finds himself in company of of men whom he considers his social inferiors, who'd risen by promotion to titles and consequence.
Secondly, Sir Walter dislikes the navy service as it ages men prematurely, so he pokes fun at Admiral Baldwin's appearance; afterall, he is only a low born man to SIr Walter !
He dismisses the Admiral by his looks; rather than consider the navy's defence of the nation.
I'm not sure how he knows the Admiral wore any powder.
Imagine if Sir Walter became bald (banish the thought!) Rank and appearance are, of course, Sir Walter's twin obessions.